Such printing presses are of the kind comprising a drum rotatably mounted at a printing station and a plurality of article holding mandrels; a feed mechanism for automatically positioning articles to be printed on the mandrels, an ejection mechanism for automatically removing the printed articles from the mandrels; drive means for effecting stepwise angular displacement of the drum, actuating means for effecting reciprocating operation of the feed mechanism, and other actuating means for effecting reciprocating operation of the ejection mechanism. Both actuating means are controlled in synchronism with the drive means.
As the drum is displaced angularly stepwise the articles to be printed which are prepositioned on drum by the feed mechanism reach in succession the printing member, i.e. a (silk) screen or a blanket roller, before they are ejected by the ejection mechanism to a collector unit adapted, for example, to convey them to a dryer. All of the foregoing operations are automatic. Such a printing machine is disclosed in French Pat. No. 1,297,842 and has met with and continues to meet with satisfaction.
It does have its drawbacks. First of all, the drive means for stepwise angular displacement of the drum includes a Geneva wheel. As is known a Geneva wheel cooperates with a drive pin and is provided with a number of notches corresponding to the number of intervals into which each revolution is divided. Accordingly it comprises as many notches as there are article holding mandrels. As a result, the structure of such a Geneva wheel and that of the drum are related.
However, depending on the diameter of the articles to be printed it may be necessary for reasons of space to vary the number of mandrels per drum, that is, to reduce the number of mandrels as the diameter increases. In this case the drum must be replaced. However, for the following reasons the Geneva wheel must also be replaced or a suitable transmission must be provided between the Geneva wheel and the drum, which is relatively time-consuming and expensive.
Furthermore, in the machine described in the aforesaid French Pat. No. 1,297,842 the means for actuating the feed mechanism and the means for actuating the ejection mechanism have a common control so that their operating speeds are identical. Consequently, if the operating speed of the machine is to be augmented the operating speeds of the feed mechanism and the ejection mechanism are correspondingly increased at the same time.
Now, if the operating speed of the feed mechanism which handles the articles to be printed may often be increased without any problems this is not the case with the operating speed of the ejection mechanism which handles articles which have been inked and therefore must be handled with care to avoid smearing the printed image. If the operating speed of the ejection mechanism is too high, vibrations of the articles may occur which are liable to interfere with the transfer conditions to the conveyor means adapted to pick them up thereby smearing the printed image.
Therefore the operating speed of such presses must normally be limited accordingly.